Mobile Genetic Elements in Sexual and Ancient Asexual Taxa

转座基因元件(TES)在真核生物和原核生物中几乎普遍存在，在多细胞真核生物中已被发现构成基因组的相当大部分：近一半在人类中，在许多植物中甚至更多。它们的存在提出了与真核基因组结构、功能和进化相关的基本问题。这个项目是基于这样一种观点，即通过比较它们在有性分类群中的特征和进化与无性分类群中的特征和进化，可以更多地了解TES及其对基因组结构的影响。由于有性繁殖在维持和限制真核生物种群中有害的TES中的重要作用，推测的无性和其他非常不寻常的特征，如在Bdelloid栖息地的干燥和再水化特征的循环中反复发生的DNA断裂和修复，使它们成为研究与TES相关的基本问题的一个很有前途的模式系统。这些问题包括它们的增殖、区隔和在基因组中的分布，它们拷贝数控制的机制，它们维持、动态和进化对双亲繁殖的依赖，它们的驯化和在维持染色体末端的可能作用，以及它们参与水平基因流动，从而TES和其他DNA可能通过不同于垂直下降的方式进入蜈蚣基因组。事实上，研究人员对蜈蚣类的研究已经揭示了与有性分类群在TE的类型和基因组分布上的显著差异，并为保护染色体及其末端不受退化的系统的操作和进化提出了新的想法。本研究的主要目的是：(1)研究蜈蚣中富含TE的亚端粒簇，以确定端粒TE拷贝是否构成抵御TES入侵的基因组防御系统的一部分，并揭示端粒相关逆转录元件在这些簇的形成和功能中所起的作用；(2)研究在蜈蚣中发现的新的逆转录酶的起源和功能及其与基因组防御机制的可能关系；(3)进一步检查蜈蚣和单体基因组中是否存在不同的完整或残留的逆转录元件和端粒富TE簇，并确定将其引入蛭体基因组的候选单体；以及(Iv)继续努力实现稳定转化，以检测引入内部和端粒区域的TES的增殖情况。这些特定的目标旨在描述蜈蚣类基因组防御的基本机制，以及它们对真核生物的普遍影响。这项研究将引起对基因组结构和进化问题感兴趣的生物学家以及普通公众的兴趣。调查人员将继续在媒体上讨论他们的研究，就像他们前几年在NPR的《联系》和《国家谈话：科学星期五》等节目中所做的那样。他们将为伍兹霍尔海洋生物实验室(MBL)的移动遗传元素簇活动做出贡献，并将参与召开一年一度的东北移动DNA会议。该项目将继续依靠学生的参与，为本科生提供动手培训，并获得在MBL独特的夏季环境的机会，其中包括著名科学家周五的讲座，以及与来访的科学家和来自世界各地的夏季课程学生互动的可能性。

Transposable genetic elements (TEs) are of virtually universal occurrence in eukaryotes and prokaryotes, and in multicellular eukaryotes have been found to constitute a substantial portion of the genome: nearly one-half in humans, and even more in many plants. Their existence raises fundamental questions related to eukaryotic genome structure, function, and evolution. This project is based on the view that much can be learned about TEs and their effects on genome structure by comparing their characteristics and evolution in sexual taxa with those in asexual taxa. Because of the important role of sexual reproduction in both the maintenance and limitation of deleterious TEs in eukaryotic populations, the putative asexuality and other highly unusual characteristics of bdelloid rotifers, such as the repeated DNA breakage and repair thought to occur during the cycles of desiccation and rehydration characteristic of bdelloid habitats, make them a promising model system for investigating fundamental problems associated with TEs. These problems include their proliferation, compartmentalization and distribution within genomes, the mechanisms of their copy number control, the dependence of their maintenance, dynamics and evolution on biparental reproduction, their domestication and possible role in the maintenance of chromosome ends, and their participation in horizontal gene flow, whereby TEs and other DNA may enter bdelloid genomes by means other than vertical descent. Indeed, the investigators' studies of bdelloid TEs have already revealed notable differences from sexual taxa in the types and genomic distribution of TEs and foreign DNA in bdelloid genomes, and have suggested novel ideas for the operation and evolution of systems that protect chromosomes and their ends from degradation. The principal objectives of the research are (i) to investigate subtelomeric TE-rich clusters in bdelloids in order to determine whether telomeric TE copies may constitute part of a genome defense system against invading TEs, and to uncover the role of telomere-associated retroelements in formation and function of these clusters; (ii) to investigate the origin and function of novel reverse transcriptases found in bdelloids and its possible relation to genome defense mechanisms; (iii) to further examine bdelloid and monogonont genomes for the presence of diverse intact or relict retroelements and telomeric TE-rich clusters, and to identify candidate monogonont TEs for introduction into bdelloid genomes; and (iv) to continue efforts to achieve stable transformation in order to test for proliferation of TEs introduced into internal and telomeric regions. These specific objectives are aimed at characterizing fundamental mechanisms of genome defense in bdelloids and their implications for eukaryotes generally. The research will be of interest to biologists interested in problems of genome structure and evolution, as well as to the general public. The investigators will continue to discuss their research in the media, as they have done in previous years on programs such as NPR's "The Connection" and "Talk of the Nation: Science Friday." They will contribute to the activities of Mobile Genetic Element Cluster at the Marine Biological Laboratory (MBL) at Woods Hole, and will participate in convening the annual Northeast Mobile DNA meeting. The project will continue to rely on student involvement, providing undergraduates with hands-on training and with access to the unique summer environment at the MBL, which includes Friday lectures by eminent scientists and the possibility to interact with visiting scientists and summer course students from around the world.